1-18. AIR SYSTEM. In this paragraph, only that part of the air system comprising air supply and storage, and driving
accessory operation is covered. Details of the remaining parts of the system are provided in paragraph 1-13, engine
governor and throttle control, paragraph 1-14, engine cooling system, paragraph 1-15, drive train, and paragraph 1-19,
a. Air Supply and Storage System.
(1) The air flow through the system is shown in figure 1-34 Filtered air is drawn from the engine turbocharger
into the compressor. Here the air is compressed and discharged via the dryer into the primary reservoir.
(2) The air flow from the primary to the secondary, emergency, and fast reservoirs is restricted by pressure
protection valves (A). These valves isolate the primary reservoir until sufficient pressure is available to permit vehicle
operation. When this pressure is obtained, pressurization of the remaining reservoirs takes place The check valves (K)
prevent backflow from the emergency and fast reservoirs once these are charged.
(3) The fast reservoir is open to the primary reservoir whenever the ignition switch is set to ON. The reservoirs
are connected via the air starter valve. This valve is operated by pilot air pressure from the fast reservoir via a solenoid
(4) To provide quick pressurization of the primary tank immediately after start up, the fast reservoir is
maintained fully charged and isolated when the ignition is OFF.
(5) During normal operation, the system is charged until maximum pressure is reached in all reservoirs. When
this occurs, the system pressure is sensed by the compressor via the (RS) line from the secondary reservoir and the
compressor starts to unload. Unloading continues until the system pressure is well below maximum. When this
happens, the unloading stops and charging continues.
(6) While the system is charging, the air flowing through the air drier is dehumidified. The moisture is
precipitated and collected in the bottom of the drier. When the compressor unloads, the discharge air opens a valve in
the bottom of the drier and the accumulated moisture is blown out by a backflow of pressurized air. This air, still hot from
compression, also removes residual moisture from the drying element.
(7) Pressure gages for the primary, secondary, and emergency reservoirs are provided in the cab.